This invention relates to plastic injection molds, and in particular, to the type of molds used to produce plastic containers and lids therefore.
In the molding of plastic containers and lids, it is usually necessary to form peripheral flanges or skirts having lateral ribs or grooves to provide interlocking engagement between the containers and lids. In order to release these articles from the mold after they are molded, it is usually necessary to have moveable molding surfaces in the mold, which are referred to as collets. The collets open up or separate upon opening of the mold to allow the molded article to be removed. The collets are opened up or separated usually by some type of push-rods or push pads engaging the collets, and normally some type of cam mechanism is used to ensure that the collets move from a closed molding position to an open release position at the appropriate time in the molding cycle. Often the collets are lifted as they are separated, as this helps to eject the molded article from the mold core as well.
A difficulty with the above-mentioned arrangement is that the collets often do not open uniformly, either as a result of uneven wear of the moving components in the mold, or differences in the actuating devices used to move the collets.
In the present invention, the collets move much more uniformly. Rather than using individual actuators to move each collet, a collet lifting ring is employed to lift all of the collets simultaneously.
According to the invention, there is provided a plastic injection mold comprising a mold core assembly and a mating mold cavity assembly. The core assembly has a core portion defining the inside surface of a plastic object to be molded in the mold, and the cavity assembly has a cavity wall defining a portion of the outside surface of the object. One of the core and the cavity assemblies includes a plurality of collets surrounding the core portion. The collets also include means for defining a portion of the outside surface of the object to be molded. The core portion, the cavity wall and the collets define a closed space between the core portion, the cavity wall and the collets in the shape of the object to be molded. One of the core and cavity assemblies has a sprue for injecting molten plastic into the closed space and an air vent to permit air to escape therefrom. Guide means engage the collets for separating and moving the collets away from the core portion upon lifting of the collets. A collet lifting ring surrounds the core portion. Means are provided for a slidably coupling the collet lifting ring to the collets, and means are provided for lifting the collet lifting ring, so that upon lifting of the collet lifting ring, all of the collets are lifted and separated simultaneously.